In general, the manufacture of a semiconductor device repeatedly involves film forming (e.g., film deposition) and etching processes performed on a surface of a substrate, e.g., a semiconductor wafer, a glass substrate, an LCD substrate, etc. For example, a film can be formed on a surface of a substrate by chemical reactions (including decomposition) of a processing gas (source gas) in a processing chamber. At the same time, the chemical reactions also generate by-products usually volatile and in gas form. The gas-form reaction by-products can be removed from the processing chamber as exhaust gas which also includes the unreacted processing gas.
The reaction by-products or the unreacted processing gas needs to be contained or treated before being discharged to the environment to prevent pollution. In addition, the discharge of the unreacted processing gas is an economic waste. Thus, a trap device (or assembly) coupled to the gas exhaust system of a film forming apparatus is used to confine and capture the reaction by-products and/or the unreacted processing gas.
Various configurations of the trap mechanism have been developed depending on the characteristics of the gas species to be trapped. For example, in the case of removing gas species that can condense at room temperature, a trap device having a plurality of trap panels in a housing is used to confine the exhaust gas. When the exhaust gas flow encounters the trap panels, the unreacted processing gas, the reaction by-products and the like can adhere to the panel surfaces and thereby be intercepted.
A trap panel typically has two opposite principle surfaces and two opposite auxiliary surfaces, where the principle surfaces have a larger area than the auxiliary surfaces. Conventionally, the principal trap surfaces of the trap panels are placed orthogonal to the flow direction of the exhaust gas to facilitate contact between exhaust gas and panel surfaces. However, in reality, the exhaust gas flow is disturbed when encountering the principal trap surfaces, causing turbulent flows. The gas molecules or other particles in a turbulent flow tend to escape from being trapped by the trap panels, which counteracts the capture effect.